1. Field of the Invention
The present invention relates to a method for promoting the crystallization of thermoplastic butene-1 polymer compositions. More particularly, this invention is related to the addition of small amounts of two specific nucleating agents to butene-1 polymer compositions, wherein the two nucleating agents cooperate in a synergistic fashion in improving the processing rate of the butene-1 polymer.
2. Description of the Prior Art
Heterogeneous nucleation via the addition of a foreign material or nucleating agent is well known. See, example, Chatterjee et al, J. Polym. Sci.; Polym. Phys. Ed., Vol. 13, 2369-83 and 2385-90 (1975). As demonstrated therein, heterogeneous nucleation is highly selective and there is no evidence of a universally strong nucleating agent for all polymers. In other words, an effective nucleating agent for one polymer may be ineffective for even a closely related polymer; similarly, even a compound closely related to an effective nucleating agent for one polymer may be ineffective for that same polymer. Chatterjee et al also disclose the use of nylons (polyamides) as nucleating agents. Nucleation and specific nucleating agents are discussed in Binsbergen, J. Polym. Sci.; Polym. Symposium, Vol. 59, 11-29 (1977).
The use of a nucleating agent to accelerate crystallization allows for faster processing and results in a more uniform microstructure because of the reduced size of the spherulites which form upon melt crystallization. The products also generally demonstrate improved physical and mechanical properties. See, for example, Rubin, Injection Molding Theory and Practice, pp. 192 (1972). In general, a desirable nucleating agent is effective at low levels of addition, both for reasons of economy and the avoidance of undue foreign structural heterogeneity which may otherwise affect the properties of the polymer.
Belgian Patent 695,803 and U.S. Pat. No. 3,756,997 disclose a variety of nucleating agents for butene-1 polymers. Specific examples include polyropylene, coumarone-indene resin, aluminum silicate, clay and aromatic sulfonic acids. Other nucleating agents are disclosed in the following copending applications: Graphitic non-turbostatic carbon nucleating agents are disclosed in copending application Ser. No. 183,869 filed Sept. 4, 1981 (having common assignee), now U.S. Pat. No. 4,321,334. Fatty acid amide nucleating agents are disclosed in copending application Ser. No. 216,055 filed Dec. 15, 1980 (having common assignee), now U.S. Pat. No. 4,322,503. These fatty acid amides include specifically N,N'-ethylene-bis-stearamide and stearamide. Anthraquinone nucleating agents are disclosed in copending patent application Ser. No. 218,865 filed Dec. 22, 1980 (having common assignee), now abandoned. Specific anthraquinones include 1,2-dihydroxy-9,10-anthraquinone; 1,4-dihydroxy-9,10-anthraquinone; 9,10-anthraquinone; and sodium 2-anthraquinone sulfonate. Amide nucleating agents are disclosed in copending application Ser. No. 214,148 filed Dec. 8, 1980 (having common assignee), now U.S. Pat. No. 4,320,209. Preferred amides include 1 -naphthalene acetamide; N-stearoyl-p-aminophenol; mercapto-N-2-naphthylacetamide; malonamide; nicotinamide; isonicotinamide; benzamide; phthalimide; salicylamide; anthranilamide; and 1,8-naphthalimide.
In U.S. Pat. No. 3,733,373 to McConnell et al, the invention is directed to improving the usefulness of butene-1 homo- or copolymers as molding resins. The patentees disclose that addition of high or medium density polyethylene substantially increases the crystallization temperature of the poly-1-butene and permits the blends to mold extremely well and to be released from the mold without being punctured or dented by the knock-out pins.
It has now been discovered that a combination of two specific additives cooperate in a synergistic fashion, resulting in much more rapid processing speeds.